1st Generation 1964 1/2 - 1973 - Questions & general discussions that apply to a specific year > 1964 1/2 - 1965

Huge flat spot on acceleration

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Hipo giddyup:
Guessing this should be where this gets posted??

  I recently rebuilt an Autolite 4100 (C5ZF-D for a 289 automatic) to use on my 66' coupe project. I have set the timing on the car (10 degrees) and it starts and runs with no issues. Now, when you give it a quick hit of the throttle, it stumbles like it is not getting enough gas or too much? I took it out around the back field and noticed that if you accelerate while driving  it will do the same thing. It even shut off twice on me. I took the top off of the carb and the bowls have plenty of gas. I also checked the accelerator pump diaphragm by removing the primary booster and with moving the throttle, gas is indeed coming up to the booster assembly (also squirts fine when the booster is replaced). I then removed the carb and replaced the power valve just to be sure it hadn't ruptured. It hadn't but I replaced it anyway. Same issue.... 
  Now I'm questioning if something else it to blame such as the vacuum advance? It had gotten too late last night to continue on so I will likely pick up where I left off tonight. I have a known good working 4100 that I was going to put in place to fully rule out a carb issue. Any thoughts or ideas on this one? It's got me stumped.... :-[

midlife:
Any chance the two booster assemblies were swapped?

jwc66k:

--- Quote from: Hipo giddyup on September 18, 2017, 09:50:01 AM ---I also checked the accelerator pump diaphragm by removing the primary booster and with moving the throttle, gas is indeed coming up to the booster assembly (also squirts fine when the booster is replaced).

--- End quote ---

--- Quote from: midlife on September 18, 2017, 01:39:10 PM ---Any chance the two booster assemblies were swapped?

--- End quote ---
Covered, but are the boosters correct? Is the accelerator pump arm in the correct hole?
Jim

preaction:
What are the factory jet sizes ?

Hipo giddyup:
 I will double check when I can get in front of my Mannel's book but yes, the boosters are correct for the carb and I would bet in the correct place. Since i was checking the booster yesterday I remember the primary was marked C H . I will say this DID NOT do this until recently. This car has sat for a few years and I am concerned there is something wrong with the distributor or vacuum advance. Maybe a bad advance plate? I did check the vacuum advance a few weeks ago (I have went over everything with a fine toothed comb) and it was not ruptured and I pulled vacuum on it. I have a new filter on the carb too so I was hoping nothing got sucked into the carb via the fuel line and clogged something? I'll let you know what I find as soon as I can. Thanks for the replies!

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